In recent years, a new concept of flight has emerged that encompasses microscale aircraft that are bio-inspired. These highly maneuverable platforms are capable of hovering flight and are ideally suited for operation in a confined environment. The reconnaissance mission envisioned for micro/nano aircraft requires a high level of autonomy due to the fast dynamics of the vehicle and the limits associated with communication in the likely areas of operation (i.e., caves and buildings).
Aerial systems that satisfy the dimensional constraints outlined by the Defense Advanced Research Projects Agency (DARPA) micro air vehicle (MAV) initiative include fixed-wing, rotary wing, and flapping-wing vehicles. The simplest and most mature of these platforms are fixed-wing vehicles that boast speed, simplicity, and well-known dynamics. However, the limitation imposed by forward flight restricts functionality in cluttered environments which can be traversed by rotary- and flapping-wing platforms.
Microscale helicopter linear dynamic system models have been developed for substantially larger vehicles, including the Yamaha RMAX helicopter. Despite the growing interest in microscale helicopter flight, a dynamic model of a single-winged rotorcraft has not been developed.
The concept of a single-wing rotating aircraft is known in the prior art. The first vehicle of this type was flown in 1952 in the woods surrounding Lake Placid, N.Y. A more recent vehicle was developed and flown by a team led by Lockheed Martin Advanced Technology Laboratories. The prototype, called MAVPro, incorporated an outrunner motor with an 8-in.-diam propeller; it weighted 0.514 kg, rotated at a stable 4 Hz, and could clime to 50 ft with radio-controlled actuation of a trailing-edge flap. The MAVPro incorporated the AG38 airfoil and exhibited a rectangular planform geometry. However, the various single-winged rotating aircraft developed over the years have made no attempt to use the most basic mode of transit of the natural Samara, e.g., the autorotation. Additionally, airfoil cross sections and planform designs have had no similarity to those found in natural Samaras.
Samaras, or winged seeds, are the sole method by which several species of plants propagate their seed. Geometric configurations for maximal seed dispersal has evolved into two main classes of seeds, both of which execute autorotational flight as they fall from the tree, and one of which additionally rotates about its longitudinal axis. The optimality of the autorotation heavily influences the population dynamics. The evolution of the Samara provides a nearly infinite set of feasible autorotation configurations with each having distinct dynamics.
Advancements in technologies associated with the sensing and control aspect of unmanned vehicles has allowed conventional micro-scaled vehicles to be equipped with real-time systems. The vast capabilities provided to these small systems are limited by the battery life and power consumption of the on-board electronics and actuators. The majority of the power consumed in an aerial system sustains a desired flight mode. The primary focus of this flight mode is to negate the effects of gravity.
A new paradigm is needed, whose focus is the design of a vehicle with a passively stable primary mode of operation which requires little or no additional power to attain/maintain this mode of transit. The natural flight of a Samara, by trading the gravitational potential energy for rotational kinetic energy which perpetuates an aerodynamically stable helical descent, is perfectly suitable for this purpose. However, no known micro-air vehicle has used this concept so far.
In addition, the conventional monocopter designs apply torque to the vehicle with a thrust device slightly offset from the ĉy axis (shown in FIG. 1). In the case of MAVPro, the propeller spins in the ĉy−ĉz plane and influences the stability about the ĉy axis. This configuration results in the propeller fighting the pitch input from the flap and reduces controllability of the vehicle. A different configuration is therefore needed which would provide an improved roll stability.